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Newbie
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Discussion Starter #1
Hi guys,

I bought myself a Gunson Gastester. I read the manual a dozen times, and it seems to work,
BUT!.....
The reason I bought it, cause I got powerfilters mounted on my carbs (not K&N, but anyway) and I don't wanna spend 100 bucks on a Jet Kit. So to proper Jet my carbs, I lowered the needle clip fully, and I taped the filters so the only have a troughput of 1/4. The bike runs very well now, no dips, and good high end. Thing is... I want to know if the Air Fuel Ratio is good balanced. Thats wy I bought the machine, but how much %CO is a good AFR ? ( I know 14:1 is good or "normal" but how does this relate to CO?)

If more info is needed, let me know guys!

Thanks in advance

Maybe a nice movie bout my new fighter is here:


Gr Jimmy
 

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Fast ZX-12R
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17,522 Posts
Nice vid.
 

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Old, bold rider
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179 Posts
CO is a general indicator of A/F ratio as it relates to the stoichoimetric ideal of 14.7:1, but it has its limitations as a tuning tool. While CO increases significantly as the A/F ratio is on the rich side of ideal, it shows little change while lean, meaning that you can tune for a minimum CO and never be sure where you are, risking engine damage. Gunson admits this, and falls back to the manufacturer's recommendations -- little help if you don't have that information.

If you are going to use this tool I'd say jet for minumum CO, then fatten it up until it starts to rise a little. That's as good as you're going to get with the tool you have.

After that you could take a bunch of plug chops to fine tune things.

There's no real shortcut to getting the jetting right.

Rob
 

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Newbie
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91 Posts
Discussion Starter #4
Thanks for the info rob,

A testing bench, is to expensive for me (50 bucks for each run!). A jet kit is also expensive... (100 bucks), I taped off the airfilters a bit more, and all 4 even. My bike has no more dips on any range, but how can I be sure its not too lean or way too rich?
 

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Newbie
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91 Posts
Discussion Starter #5
Thanks for the info rob,

A testing bench, is to expensive for me (50 bucks for each run!). A jet kit is also expensive... (100 bucks), I taped off the airfilters a bit more, and all 4 even. My bike has no more dips on any range, but how can I be sure its not too lean or way too rich?
My bike has no more dips on any range, but how can I be sure its not too lean or way too rich?
and btw, i guess I can sell that stupid CO tester ?
 

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Old, bold rider
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179 Posts
My bike has no more dips on any range, but how can I be sure its not too lean or way too rich?
and btw, i guess I can sell that stupid CO tester ?
If the CO tester can be portable it may still be useful -- if, however, you can't load the motor and check for CO levels without spending a bundle on dyno time then chuck it.

As to the mixture strength, taping the filters can be used as a tuning tool only insofar as it will tell you where the present jetting is. If it's chuffing soot then you were rich to begin with, and conversely if it starts running good then you're lean. Using this as a guideline you can assume that you're going to have to fatten things up across the board when the tape is removed, which should be done ASAP. How far to go is problematic as CV carbs (I assume you are running CV carbs) are airflow sensitive, so restricting the filters changes the slide's reactions at a particular throttle / RPM. Frankly, I have little experience with CV carbs -- my mantra is "Throw a set of flatslides on it and dial them in!" Not much help for those amongst you who don't have a grand or so to throw at the problem.

If you have access to jets then the project is comparatively easy, if a bit time consuming.

If not you're bucks ahead by getting a jet kit from a known source and throwing it in. You'll have to do some plug chops to check, but since most of them won't be at redline in top gear it shouldn't be a problem. Just try to hold the motor in a particular range where it's "not running right" for as long as possible, then pull in the clutch and hit the kill switch. The condition of the plugs will tell you which way to take the jetting and / or needle position to bring it into an acceptable range.

Just remember to get the main jets close to right first -- everything else depends on this.

Bon Chance

Rob
 

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Newbie
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Discussion Starter #7
Thanks Rob,

I'm gonna sell the gas tester, and get me a jet kit (€95 euro's for my bike). I don't wanna go to a test bench or something cause I already gone over my budget building this bike, and I already did a factory pro jet-kit on my dad's rex1100, and I got a decent setup just from the advice from the jet kit. Only thing I want to avoid is running too lean since it can damage my cilinders, U think I can get a "safe" setup with the dynojet kit but without going to a testing centre?


Greetz Jimmy
 

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Old, bold rider
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179 Posts
Thanks Rob,

I'm gonna sell the gas tester, and get me a jet kit (€95 euro's for my bike). I don't wanna go to a test bench or something cause I already gone over my budget building this bike, and I already did a factory pro jet-kit on my dad's rex1100, and I got a decent setup just from the advice from the jet kit. Only thing I want to avoid is running too lean since it can damage my cilinders, U think I can get a "safe" setup with the dynojet kit but without going to a testing centre?


Greetz Jimmy
Most jet kits are set up on the fat side to prevent liability issues. As long as they have kits for various accessory levels, such as stock, with an exhaust, exhaust and air filters, cams, ETC. then you can be relatively sure you're not going to be too lean. Nonetheless, do a series of plug chops to be sure -- in the final analysis you're responsible for it's being right.

Rob
 

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Newbie
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Discussion Starter #9
I sold my tester 2day, gonna call the local dynojet/factory pro dealer to order me a Kit.
Thanks for the help guys... think this topic is closed....
 
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